Conventional polymethylmethacrylate bone cements (PMMA bone cements) are usually made from a powdered component and a liquid monomer component (K.-D. Kühn: Knochenzemente für die Endoprothetik: ein aktueller Vergleich der physikalischen and chemischen Eigenschaften handelsublicher PMMA-Zemente. Springer-Verlag Berlin Heidelberg New York, 2001). After mixing the cement powder with the liquid monomer component, said PMMA bone cements are applied in their non-cured pasty state in the form of a cement dough. If mixing systems are used with powder-liquid cements, the cement dough is situated in a cartridge. The cement dough is squeezed from said cartridge through the motion of a feed plunger. A motion of the feed plunger of this type can be effected by means of a mechanical application device.
In the case of pasty two-component pastes and/or two component bone cements, such as are known, for example, from DE 10 2007 050 762 B3, DE 10 2008 030 312 A1 or DE 10 2007 052 116 B4, both pasty components are stored in two separate cartridges with two separate feed plungers. During application, both pastes are pressed from the interior spaces of the cartridge into a static mixer through the motion of the feed plungers and are dispensed through a dispensing tube once the mixing is completed.
The application of pasty adhesives and sealants is done basically the same way using paste application devices.
Currently, paste application devices that can be driven manually or pneumatically or electrically are used to extrude thick viscous masses. Customary simple mechanical paste application devices utilise, in particular, clamp rods that are driven by a manually-operated tilting lever for extrusion. In the case of highly viscous pastes, said devices can be operated only by exerting very strong forces. This exertion of force is unreasonable for medical users in the OR.
Electrically-driven extrusion devices can be driven both with rechargeable batteries and/or batteries or by means of a stationary electrical power supply. Said devices can extrude particularly thick pasty masses since their force is very large in some cases. However, it is one disadvantage of the use of electrical motors that these motors contain non-ferrous metals and are expensive. Moreover, rechargeable batteries must be kept in stock or a cable connection, which is an impediment in the OR area, must be provided by means of which the paste application device must be connected to a power network.
Pneumatic paste application systems, like the systems known, for example, from U.S. Pat. No. 2,004,074 927 A1 or U.S. Pat. No. 6,935,541 B, require a compressed air connection. This necessitates compressed air hoses, which may impede the mobility of the user and the use of the paste application system. Alternatively, the use of compressed gas cartridges to provide compressed gas is feasible just as well. Documents U.S. Pat. No. 2,818,999 A and EP 1 118 313 A1 shall be cited as being exemplary in this context.
An interesting proposal is described in EP 4 925 061 A1. This system has no gas cartridge arranged in the device. The device needs to be filled with compressed gas by means of a valve prior to its application. Aid device contains a cartridge, in which the viscous mass is arranged. A plunger that is connected to one end of the cartridge by means of a bellows is arranged behind the viscous mass. Before application, a liquid gas is filled through a valve into the hollow space formed by the plunger, the bellows, and the cartridge end. This proposal has to be seen in a critical light, since the expansion of liquid gas is associated with cooling which may lead to the elastic bellows becoming brittle. If the bellows becomes brittle, leakiness cannot be excluded. As a result, compressed gas can exit through the bellows and penetrate into the viscous mass adjacent to the plunger. Any mixing of the pastes with compressed gas is inacceptable in the case of polymethylmethacrylate bone cement pastes. Gas bubbles would weaken the cured polymethylmethacrylate. Moreover, the liquid compressed gas is difficult to fill into the receptacle and it is unreasonable to expect users in the OR to do this.
DE 10 2010 019 223 B4 proposed a cementing device, in which a compressed gas cartridge is punctured by means of the motion of a rotary valve. The compressed gas presses directly onto the plunger of the device. The dispensation of the pastes is regulated by a valve. It is a advantage of said device that high-strength plastic materials need to be used for the cartridges, since no pressure vessel is provided.
Basically, it is feasible with all compressed gas-driven paste application devices having feed plungers that the compressed gas passes by the feed plunger into the pastes in unwanted manner. This issue may be more pronounced the higher the gas pressure is.
Moreover, devices for the dispensation of medications are known from the field of medicine that also utilise compressed gas cartridges as energy source, although no regulation of the volume flow of the medication by means of valves is provided (U.S. Pat. No. 2,008,086 079 A1, U.S. Pat. No. 2,008,208 114 A1). Systems of this type are not very useful for bone cements, since they do not allow for specific portioning of the bone cement dough during the operation.